Fig. 1. (a) Electric current distribution on our first-generation atom chip in U-MOT configuration (a Z-wire and an end-wire are switched on simultaneously). Red arrows show directions of current flow. (b) Electric current distribution on our new-generation atom chip. Only the wide U-wire is switched on. Red arrows show directions of current flow. (c), (d) Magnetic field distribution in the plane perpendicular to the narrow/wide wires’ central parts. Black lines show magnetic field axes of the ideal quadrupole field. The bottom of the figure shows the total current I through microwires and external magnetic field B for each case.

Fig. 2. The experimental scheme for loading U-MOT near the atom chip. The energy level diagram of ⁸⁷Rb atoms and frequencies of cooling and repumping lasers are shown at the right bottom.

Fig. 3. The atom chip. The chip dimensions are 25 mm × 25 mm. The chip is covered mostly by metal so that its surface could function as a mirror. Each chip microwire is bonded by a set of narrow (50 µm diameter) gold wires to the electrical contacts. The silicon substrate of the chip is mechanically pressed to the copper holder in the corners.

Fig. 4. Images of atomic clouds of ⁸⁷Rb localized near the new atom chip. Images were acquired through detection of atomic luminescence by sCMOS camera. Left: optimized narrow-wire U-MOT. Right: optimized wide-wire U-MOT. The ratio of the number of localized atoms is approximately 1:3.5.

Fig. 5. The process of atomic cloud reloading from the wide-wire U-MOT into the narrow-wire U-MOT. Operating parameters are switched from I_wide = 8 A, I_narr = 0, B = (5; 0; −2.1) G to I_wide = 0, I_narr = 3 A, B = (3.5; 0; −1.6) G, rapidly at t = 0 ms.